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SKULL AS A WHOLE + CRANIAL FOSSAE LEARNING OBJECTIVES At the end of this lecture , the student should be able to know: • • • • • • • • • • • Parts of skeleton (axial and appendicular) Parts of skull Sutures of skull Different bones of skull Different views (Norma) of skull Interior of the skull Divisions of the cranial fossa Anterior cranial fossa Foramens and strucutures passing through them Middle, and posterior cranial fossa Foramens and structures passing through them The Axial Skeleton • Eighty (80) bones • It is composed of five parts; – – – – – Skull Ossicles of the middle ear Hyoid bone of the throat Vertebral column Bony thorax The Axial Skeleton The skull • The skull, body’s most complex bony structure, is formed by the cranium and facial bones (bones of face) • Cranium – – cranium encloses cranial cavity – protects the brain and is the site of attachment for head and neck muscles • Facial bones – – Supply the framework of the face, the sense organs, and the teeth – Provide ,surround and protect the entrances to the respiratory and digestive tracts – Anchor the facial muscles of expression Bones of skull • Formed from eight large bones – Paired bones include • Temporal bones • Parietal bones – Unpaired bones include • Frontal bone • Occipital bone • Sphenoid bone • Ethmoid bone Overview of Skull Geography • The skull contains approximately 85 named openings – Foramina, canals, and fissures – Provide openings for important structures • Spinal cord • Blood vessels serving the brain • 12 pairs of cranial nerves SUTURES • A suture is a type of fibrous joint which only occurs in the skull (or "cranium"). • A tiny amount of movement is permitted at sutures, which contributes to the compliance and elasticity of the skull. • Main sutures are: – – – – – Sagittal Coronal or Frontal Squamosal Lambdoidal Sutural (Wormian) Bones • Usually found in Lambdoidal suture SUTURES OF LATERAL SIDE SUTURES OF OCCIPITAL REGION FONTANELLES IN NEWBORN • Fontanelles are soft spots on a baby's head which, during birth, enable the bony plates of the skull to flex, allowing the child's head to pass through the birth canal. • The ossification of the bones of the skull cause the fontanelles to close over by a child's second birthday. • The closures form the sutures of the neurocranium. FONTANELLES FONTANELLES STUDY OF SKULL Skull can be studied from different views.The views so obtained are termed the normae of the skull – From Above- Norma Verticalis – From Below- Norma Basalis – From Front- Norma Frontalis – From Back- Norma Occipitalis – From Side- Norma Lateralis – From Inside – Interior of skull SKULL SUPERIOR VIEW (NORMA VERTICALIS) • Four sutures mark the articulations of the parietal bones – Coronal suture – articulation between parietal bones and frontal bone anteriorly – Sagittal suture – where right and left parietal bones meet superiorly – Lambdoid suture – where parietal bones meet the occipital bone posteriorly – Squamosal or squamous suture – where parietal and temporal bones meet INFERIOR VIEW OF THE SKULL (NORMA BASALIS) THE SKULL ANTERIOR VIEW (NORMA FRONTALIS) • oval outline • Limited – above by the frontal bone – below by the body of the mandible – laterally by the zygomatic bones and the mandibular rami. SKULL POSTERIOR VIEW (NORMA OCCIPITALIS) • Circular outline. • Forms most of skull’s posterior and base • Major markings include – – – – – – – Sagittal suture Lamboidal suture external occipital protuberance mastoid foramen foramen magnum, occipital condyles hypoglossal canal Skull: Lateral View (Norma Lateralis) • Form most of the superior and lateral aspects of the skull MIDSAGITTAL LATERAL ASPECTS OF THE SKULL INTERIOR OF THE SKULL (CRANIAL FOSSA) THE CRANIAL FOSSAE Cranial fossa – curving depression of the cranial floor • Anterior cranial fossa formed by: • frontal bone, ethmoid, lesser wing of the sphenoid; cradles the frontal lobes of the cerebral hemispheres Middle cranial fossa is formed by: sphenoid, temporal, parietal bones; cradles the temporal lobes of the cerebral hemispheres, the diencephalon, and mesencephalon • Posterior cranial fossa is formed primarily by: occipital bone, with contributions from the temporal and parietal bones - suports the occipital lobes of the crebral hemispheres, the crebellum, and the pons and medulla oblongata (brain stem) THE SECTIONAL ANATOMY OF THE SKULL THE CRANIAL FOSSAE INTERIOR OF THE CRANIAL CAVITY • Cranial cavity: occupied by the brain • Calvaria (skull cap): upper dome-like portion of skull • Floor divided into anterior, middle, and posterior fossae • Crista galli: prominent ridge in center of anterior fossa. Point of attachment for the dura mater (one of the meninges) INTERIOR OF THE CRANIAL CAVITY • Olfactory fossae lateral to crista galli. Olfactory bulb within – Cribriform plate of the ethmoid forms floor of olfactory fossae – Olfactory nerves pass through the foramina of the cribriform plate • Sella turcica: part of sphenoid bone that houses the pituitary gland • Foramen magnum: opening where brain attaches to spinal cord ANTERIOR CRANIAL FOSSA • The floor of the anterior fossa is formed by: – Orbital plates of the frontal, – Cribriform plate of the ethmoid – small wings and front part of the body of the sphenoid • It is limited behind by the posterior borders of the small wings of the sphenoid and by the anterior margin of the chiasmatic groove. • It is traversed by the frontoethmoidal suture sphenoethmoidal suture sphenofrontal sutures. ANTERIOR CRANIAL FOSSA • The central portion corresponds with the roof of the nasal cavity, and is markedly depressed on either side of the crista galli. • It presents, in and near the median line, from before backward, the commencement of the frontal crest for the attachment of the falx cerebri • Foramen cecum, – The frontal crest of the frontal bone ends below in a small notch which is converted into a foramen, by articulation with the ethmoid – It transmits a vein from the nose to the superior sagittal sinus ANTERIOR CRANIAL FOSSA • Crista galli, ridge behind the foramen cecum, the free margin of which affords attachment to the falx cerebri • Olfactory groove on either side of the crista galli, formed by the cribriform plate, • Supports the olfactory bulb and presents foramina for the transmission of the olfactory nerves, • In front a slit-like opening for the nasociliary nerve. ANTERIOR CRANIAL FOSSA • Anterior ethmoidal foramen – situated about the middle of the lateral margin of the olfactory groove, – Transmits the anterior ethmoidal vessels and the anterior ethmoidal nerve • Posterior ethmoidal foramen – Opens at the back part of this margin under cover of the projecting lamina of the sphenoid – transmits the posterior ethmoidal vessels and nerve Identify?? Middle cranial Fossa • Deeper than the preceding, is narrow in the middle, and wide at the sides of the skull. • It is bounded • in front by the posterior margins of the small wings of the sphenoid, the anterior clinoid processes, ridge forming the anterior margin of the chiasmatic groove; • behind, by the superior angles of the petrous portions of the temporals and the dorsum sella • laterally by the temporal squama, sphenoidal angles of the parietals, and great wings of the sphenoid. Middle cranial Fossa • It is traversed by the – squamosal, – sphenoparietal, – sphenosquamosal, – sphenopetrosal sutures. Middle cranial Fossa • Chiasmatic groove – The superior surface of the body of the sphenoid bone is bounded behind by a ridge, which forms the anterior border of a narrow, transverse groove, the chiasmatic groove (optic groove) • Tuberculum sella – In the sphenoid bone, behind the chiasmatic groove is an elevation, the tuberculum sellæ Middle cranial Fossa • sella turcica – Deep depression Behind the tuberculum sella – Contains the fossa hypophyseos, which lodges the hypophysis, and presents on its anterior wall the middle clinoid processes – Bounded posteriorly by a quadrilateral plate of bone, the dorsum sella, upper angles are surmounted by the posterior clinoid processes – Gives attachment to the tentorium cerebelli, and below each is a notch for the abducent nerve – On either side of the sella turcica is the carotid groove Middle cranial Fossa • Optic foramen – The optic foramen is the opening to the optic canal. – Transmits the optic nerve and ophthalmic artery (with accompanying sympathetic nerve fibres) into the orbital cavity. • Behind the optic foramen the anterior clinoid process is directed backward and medialward and gives attachment to the tentorium cerebelli Middle cranial Fossa • Superior orbital fissure • Bounded – – – – Above by the small wing Below, by the great wing, Medially, by the body of the sphenoid Laterally by the orbital plate of the frontal bone. • Transmits to the orbital cavity • oculomotor, trochlear, ophthalmic division of the trigeminal, abducent nerves, some filaments from the cavernous plexus of the sympathetic, the orbital branch of the middle meningeal artery; • From the orbital cavity • Recurrent branch from the lacrimal artery to the dura mater, and the ophthalmic veins Middle cranial Fossa • Foramen rotundum – Behind the medial end of the superior orbital fissure – Provides passage of the maxillary nerve. • Foramen ovale – At base of lateral pterygoid plate – Through which passes mandibular nerve, accessory meningeal artery, & lesser petrosal nerve • Foramen spinosum – Posterior & somewhat lateral to foramen ovale – Transmits middle meningeal vessels & small meningeal branch of mandibular nerve Middle cranial Fossa • Foramen lacerum – At base of medial pterygoid plate in dried skull – Not complete foramen in intact body, because its inferior part is covered over by fibrocartilaginous plate, across superior (inner or cerebral) surface of which passes internal carotid artery. • Carotid canal – Inferior surface of petrous temporal bone is pierced by round opening. – Internal carotid artery, coursing within canal, immediately takes right angle turn to reach side of foramen lacerum. Middle cranial Fossa Hiatus for greater petrosal nerve (or hiatus of the facial canal) • A shallow groove, sometimes double, leading lateral and backward to an oblique opening for the passage of the • greater superficial petrosal nerve • petrosal branch of the middle meningeal artery. Middle cranial Fossa • Facial canal is a Z-shaped canal running through the temporal bone from the internal acoustic meatus to the stylomastoid foramen. • In humans it is approximately 3 centimeters long, which makes it the longest human osseous canal of a nerve • It is located within the middle ear region, according to its shape it is divided into three main segments: the labyrinthine, the tympanic, and the mastoidal segment. Posterior cranial Fossa • The posterior fossa is the largest and deepest of the three. • It is formed by – – – – Dorsum sella and clivus of the sphenoid Occipital Petrous and mastoid portions of the temporals Mastoid angles of the parietal bones • Crossed by the – occipitomastoid suture – parietomastoid sutures • lodges the cerebellum, pons, and medulla oblongata. Posterior cranial Fossa • Foramen magnum – Posterior to basilar portion of occipital bone – Transmit - Medulla oblongata & its membranes Accessory nerves Vertebral arteries Anterior & posterior spinal arteries Ligaments connecting occipital bone with axis Posterior cranial Fossa • Hypoglossal canal – Courses forward & laterally from inner aspect of occipital bone within cranium just above foramen magnum to opening that perforates occipital bone externally at lateral part of base of occipital condyle – Transmits hypoglossal nerve &a branch of posterior meningeal artery Posterior cranial Fossa • The jugular foramen is situated between the lateral part of the occipital and the petrous part of the temporal – Anterior compartment – inferior petrosal sinus – Intermediate – glossopharyngeal, vagus, & accessory nerves – Posterior – sigmoid sinus which leads to internal jugular vein, & some meningeal branches from occipital & ascending pharyngeal arteries Posterior cranial Fossa • The internal auditory meatus (also internal acoustic meatus,) is a canal in the petrous part of the temporal bone of the skull that carries nerves from inside the cranium towards the middle and inner ear compartments • Namely cranial nerve VII and cranial nerve VIII. 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